A relatively new category of respiratory protective equipment is the Chemical, Biological Radiological, and Nuclear (CBRN) Air-Purifying Escape Respirator (APER). Additional details on this category of equipment are available via the National Institute for Occupational Safety and Health (NIOSH) standard dated Sep. 30, 2003.
A major component of the CBRN APER is the CBRN protective hood. CBRN protective hoods are comprised of four major component parts: (1) an elastic neck dam; (2) a visor; (3) a harness and (4) a hood body (the entire hood excluding the neck dam, harness and visor). CBRN protective hoods (the hood body) can be made from lightweight film composites, such as TYCHEM® film composites sold by Dupont and ZYTRON® film composites sold by Kappler. Lightweight film composites (LFCs) offer many significant advantages over other barrier materials, such as PVC and butyl coated fabric. The advantageous characteristics of LFCs are as follows:
Thin and flexible material;
Can be heat fused to itself to form gas tight seams;
Excellent chemical holdout capability;
Excellent particulate holdout capability;
Can be hard folded and tightly compacted to minimize package size;
Will not take a hard set during desert storage conditions;
Will not yellow with aging;
Will not shatter when flexed in artic conditions; and
Can easily be interfaced with polyester (MYLAR® material), which is a preferred visor material.
MYLAR® material provides highly desirable optics, chemical resistance and anti-fog properties in view of competing visor materials. Other visor materials include PVC and Urethane.
The main disadvantage of LFC's is the problem of interfacing an elastomeric neck dam. The neck dam is an essential component of the CBRN protective hood. The neck dam can be made from neoprene, butyl, silicone or other elastic materials. The neck dam forms the bottom of the hood and provides the critical seal between the hood and the wearers' neck.
In normal use, the center hole in the neck dam is stretched open and then the entire hood is pulled over the wearers head. The neck dam is then released so that it can conform and seal to the wearers neck. The neck dam blocks contaminated air from entering the inside of the hood, and thus protects the wearer's entire head.
There must be a bond between the neck dam and the hood barrier material which is both mechanically strong and fluid tight. LFC's have a backing that is comprised of non-woven fibers which are permeable to air. The advantage of the fibers is that they provide a good attachment point for adhesive. The adhesive is able to encapsulate and lock onto the surface layer of fibers, which in turn provides a mechanically strong bond between the LFC and the elastic neck dam. However, the adhesive is not able to penetrate the entire layer of fibers and does not provide a gas tight seal.
Therefore, there is a need for a gas tight interface between LFC's and an elastic neck dam. The gas tight seal should withstand numerous challenges including:
(1) Hard folding and creasing;
(2) Tight vacuum compaction;
(3) 5 years of desert storage (71 C);
(4) 5 years of artic storage (−46 C);
(5) 5 years of cyclic storage (desert/arctic/desert);
(6) Mechanical stress during the hood donning process;
(7) Desert unfolding & donning;
(8) Artic unfolding & donning;
(9) Exposure to toxic chemical gases;
(10) Exposure to toxic biological particles;
(11) Exposure to toxic radiological particles;
(12) Shock; and
(13) Vibration.
Some protective hoods are made from PVC. PVC is a monolithic material that provides a solid and smooth surface to which an elastic neck dam can be bonded. The primary advantage of a PVC hood is that an elastic neck dam can be glued to the PVC material without a gas leak path caused by fibers. The adhesive will bond the PVC and elastic neck dam together and will also seal the gap between the two materials to prevent air or other gases from passing between the between the two materials. However, a PVC hood has many disadvantages.
PVC does not lend itself to the combination of hard folding, vacuum compaction, artic storage, desert storage or cyclic storage. Adhesive does not stick very well to PVC so the adhesive bond between PVC and an elastomeric neck dam will have limited mechanical strength. Typically, a neck dam can be separated from PVC with minimal force.
The weak bond strength between a PVC hood body and an elastic neck dam prevents a PVC protective hood from being hard folded in order to meet package size requirements for some government applications. PVC will shatter if unfolded at temperatures below freezing. PVC will take a hard set when stored in desert conditions. PVC visors cannot be treated with a permanent anti-fog. Polyester (MYLAR) visors that are treated with permanent anti-fog coatings such those sold under the brand name VISTEX by Film Specialties, Inc. cannot be fused or glued to PVC. Because PVC hoods do not lend themselves to hard folding, the resulting hooded respirators that use PVC hoods have a very large package size which makes them much less convenient to store, transport and carry.
In contra-distinction, hoods made from ZYTRON® material can be hard folded. The ZYTRON® material is much thinner, lighter and more flexible than PVC. ZYTRON® material does not take a set in hot storage and will not shatter when unfolded in artic conditions. A polyester (MYLAR®) visor coated with VISTEX® permanent anti-fog coating can easily be sealed to the ZYTRON® non-woven backing. ZYTRON® material is a more efficient chemical barrier than either PVC or butyl coated fabric.
A previous disadvantage of ZYTRON® material is that it is not a monolithic material and it does not provide a solid and smooth surface to which an elastic neck dam can be bonded and sealed. ZYTRON® is a composite material with a chemical barrier film on the outside and an air permeable material on the back side. The air permeable material is referred to as “non-woven” or “spun bond”.
The non-woven backing, when examined under a microscope, is comprised of loosely packed fibers. Air, other gases and particles can easily pass laterally through the loose fibers. When an adhesive is applied to the non-woven substrate it is able to interlock with some of the fibers, but it is not able to penetrate and seal all of the fibers. Adhesives known in the art provide good mechanical bonds but do not provide a gas tight seal. The non-woven fibers can be melted and sealed to each other. However, the adhesive does not bond to slick, monolithic plastic, such as polypropylene. Thus, there exists a long-felt, but heretofore unfulfilled need in the art to create a gas tight seal between “non-woven” and elastic material without giving up the mechanical bond strength.
It should be noted that a gas tight material interface described herein can be used in various Chemical Biological Radiological Nuclear (CBRN) protective garments, including a protective hooded respirator.